Immunotherapy - Active immunity and passive immunity

Immunotherapy 
The immune system can be manipulated to help people avoid or recover from diseases. Some of these techniques have been utilized for a long time, and others are relatively new.
Active Immunity 
Active immunity, which provides long-lasting protection against a disease-causing organism, develops after an indi­vidual is infected with a virus or bacterium. In many in­stances today, however, it is not necessary to suffer an illness to become immune because it is possible to be arti­ficially immunized against a disease.
Immunization involves the use of vaccines, sub­stances that contain an antigen to which the immune system responds. Traditionally, vaccines have been the pathogens themselves, which have been treated so that they are no longer able to cause disease. New methods of producing vaccines, however, are being developed through biotechnology. For example, as discussed in the Medical Focus reading on the next page, biotechnology is responsi­ble for a new hepatitis B vaccine. Vaccines for other serious illnesses, such as malaria, Lyme disease, and AIDS, are also being developed. The MedAlert reading on page 264 dis­cusses the AIDS vaccine.
After a vaccine is given, it is possible to determine the amount of antibody present in a sample of blood serum, which is called the antibody titer (ti'ter). A primary re­sponse follows the first exposure to an antigen. For a pe­riod of several days, no antibodies are present; then, there is a slow rise in the titer, followed by a gradual decline.
A secondary response may occur after a second expo­sure. If so, the titer rises rapidly to a level much greater than before. The second exposure is often called the booster be­cause it "boosts" the antibody titer to a higher level The antibody titer then may be high enough to prevent disease symptoms even if the individual is exposed to the disease. If so, the individual is immune to that particular disease.
A good secondary response can be related to the num­ber of plasma cells and memory cells in the blood serum. Although it is customary to test the serum, the memory cells in lymph nodes and the spleen are probably more im­portant than those that are blood-borne. Upon second ex­posure, these cells are already present, and antibodies can be produced rapidly.
Active (long-lived) immunity can be induced by vaccines when a person is well and in no immediate danger of contracting an infectious disease. Active immunity is dependent upon the presence of memory cells in the 
body. 
Passive Immunity 
Passive immunity occurs when an individual is given anti­bodies (immunoglobulins) to combat a disease. Since these antibodies are not produced by the individual's B cells, passive immunity is short-lived. For example, new­born infants possess passive immunity because antibodies have crossed the placenta from the mother's blood. These antibodies soon disappear, however, so that within a few months, infants become more susceptible to infections. Breast-feeding prolongs the passive immunity an infant re­ceives from the mother because of antibodies in the mother's milk.
Even though passive immunity does not last, it is occa­sionally used to prevent illness in a patient who has been unexpectedly exposed to an infectious disease. Usually, the person receives an injection of an antibody-containing serum that may have been taken from donors who have re­covered from the illness. In the past, horses were immu­nized, and serum was taken from them to provide the antibodies needed to combat diphtheria, botulism, and
tetanus. Occasionally, a patient who received these anti­bodies developed a disease called serum sickness, indicat­ing that the serum contained proteins that the individual's immune system recognized as foreign.
A new method of producing antibodies has been de­veloped. Lymphocytes are removed from the body and ex­posed in vitro (in laboratory glassware) to a particular antigen. The stimulated lymphocytes are fused with a cancer cell so that they continuously divide, producing a clone of cells capable of making only one type of antibody. These antibodies, called monoclonal (mon" 0- klan' al) antibod­ies, do not cause serum sickness.
Passive immunity is needed when an individual is in immediate danger of succumbing to an infectious disease. Passive immunity is short-lived because the antibodies are administered to and not made by the individual.
Lymphokines 
Lymphokines (also called cytokines) are the immunostim­ulatory proteins released by T cells. They are being investi­gated as possible adjunct therapy for cancer and AIDS because they stimulate white blood cell formation and/or function. Both interferon and various other types of lym­phokines called interleukins have been used as im­munotherapeutic drugs, particularly to potentiate the ability of the individual's T cells (and possibly B cells) to fight cancer.
Interferon is a sub­stance produced by leukocytes, fibroblasts, and probably most cells in response to a viral infection. When produced by T cells, interferon is called a lymphokine. Interferon is still being investigated as a possible cancer drug, but so far, it has proven effective only in certain patients, and the ex­act reasons as yet cannot be discerned.
Theoretically, cancer cells that carry an altered protein on their cell surface should be attacked and destroyed by killer T cells. The presence of a developing cancer may in­dicate that killer T cells have not been activated. In that case, lymphokines might awaken the immune system and lead to the cancer's destruction. In one technique being in­vestigated, researchers first withdraw T cells from the pa­tient and activate the cells by culturing them in the presence of an interleukin. The cells are then reinjected into the patient, who is given doses of interleukin to main­tain the killer activity of the T cells.
Those who are actively engaged in interleukin research believe that interleukins soon will be used as adjuncts for vaccines, for the treatment of chronic infectious diseases, and perhaps for the treatment of cancer. Chemicals that block the actions of interleukins may prove helpful in pre­venting skin and organ rejection, autoimmune diseases, and allergies.
The interleukins and ather Iymphakines shovv some promise of potentiating the individual's ovvn immune system.